This invention relates to an apparatus and method for working asphalt pavement. More specifically, this invention relates to a rotary tool that is spun at high speed and applied to the pavement, thereby locally heating the pavement to a temperature sufficient to work the pavement adjacent the rotary tool.
In this application, “asphalt pavement” refers to the compact, wear resistant surface that facilitates vehicular, pedestrian, or some other form of traffic, such as along roadways, streets, highways, freeways, shoulders, raceways, parkways, trails, pathways, runways, tarmacs, parking lots, ramps, driveways, alleyways, sidewalks, and crossings.
The asphalt pavement may comprise some or all of oil, tar, tarmac, macadam, tarmacadam, asphalt, asphaltum, pitch, bitumen, minerals, rocks, pebbles, gravel, sand, polyester fibers, and petrochemical binders. The asphalt composition is usually heated, laid down, compacted, and finished to provide a paved, traffic-worthy surface.
Once the asphalt pavement is in place, it remains in a plastic state, and its wear resistance is affected by ambient conditions such as heat and moisture, erosion, and traffic usage. High ambient temperatures may cause the otherwise hard surface to soften, expand, and plastically deform under the weight of heavy-weight vehicular traffic. Therefore, it is not unusual to find depressions and ruts in asphalt paved surfaces resulting from the passage of the heavy-weight vehicles on a hot day. Low ambient temperatures cause the asphalt pavement to contract and crack. Under freeze thaw conditions, the expansion and contraction of the pavement causes the aggregate components in the asphalt pavement to separate, resulting in surface wear. Moisture trapped beneath the asphalt pavement or seeping up through the pavement also may contribute to the deterioration of the paved surface.
The effects of weather, moisture, and high traffic combine to wear away the asphalt pavement. Wear usually manifests itself in the form of loosened asphalt materials on the surface of the pavement, surface and subsurface cracks and voids, and pot holes.
In traffic areas repairs and maintenance of paved surfaces is an ongoing process that is somewhat problematic. First of all, the mere presence of labor, materials, and equipment in traffic areas is hazardous. Secondly, because of its chemistry, used asphalt pavement is classified as a hazardous material and is difficult to dispose of. Therefore, it is preferred to recycle used asphalt pavement, but this requires expensive and complex systems for removing the pavement from the roadbed, transporting the asphalt to a recycling area, grinding up the asphalt and reconditioning it suitable for reuse; and then transporting to where it will be reapplied.
Another difficulty in repairing and maintaining asphalt pavements is the presence of utility easements and boxes, manholes and manhole covers, culverts, rails, curbs, gutters, and other non-asphalt obstacles that are found in modern road ways. Negotiating around these man-made obstacles is time consuming, labor intensive, and also dangerous.
Maintenance and repair of asphalt pavement may comprise a multi-step process including heating the paved surface; mechanically decomposing or breaking up the asphalt surface; applying reconditioning materials to the decomposed asphalt; reapplying the reconditioned asphalt to the road surface; and compacting and finishing the asphalt surface to the desired specifications.
Numerous systems have been proposed to accomplish each step in the maintenance and repair process for asphalt pavement. The following patents are exemplary of such systems.
U.S. Pat. No. 3,970,404, to Benedetti, teaches a method for the reconstruction of asphalt pavement. The method includes heating the pavement in successive stages so that it may be heated to a working temperature without overheating that would lead to deterioration of the asphalt properties.
U.S. Pat. No. 4,018,540, to Jackson, Sr., discloses a road maintenance machine with a heater assembly mounted on a general purpose chassis. The heater includes multiple burners, exhaust hoods, and heat shields in order to direct the generated heat and gases onto the pavement. The chassis is provided with additional hydraulic equipment to assist the road maintenance process such as adjustable planer and scarifier to work the heated asphalt. An elevator is provided at the rear of the machine to remove the asphalt debris from the roadway.
U.S. Pat. No. 4,104,736, to Mendenhall, teaches an improved asphalt-aggregate recycling process by direct exposure of the asphalt to hot gases of combustion to form a gaseous exhaust mixture, and subjecting the gas mixture to a centrifugal force sufficient to separate out the hydrocarbon particulates for recycling.
U.S. Pat. No. 4,335,975, to Schoelkopf, discloses a method for resurfacing roads whereby the road surface is first plastified and broken-up by first and second separable devices. The broken-up material is immediately distributed, rearranged, and contoured onto the road surface by the second device without the introduction of fresh asphalt or bituminous material. A repaver apparatus forming a third separate device then applies fresh asphalt or bituminous material onto the broken-up, rearranged material. Preferably, two distributions of broken-up material are employed prior to the asphalt application and compaction of the new asphalt material.
U.S. Pat. No. 4,407,605, to Wirtgen, describes, inter alia, an apparatus comprising a chassis including its own drive engine and at least one heating device and means for loosening the road coating arranged behind it. The means for loosening the road coating is a small roller provided with chisels and rotating in the direction opposite the direction the chassis is going. The roller is arranged in a discharge area of a container holding new coating material such that when rotating, the roller compounds old material with new material.
U.S. Pat. No. 4,601,605, to Damp et al., teaches a scarifier for use with an asphalt roadway surface. The scarifier features a number of heaters of the luminous wall type in order to direct large quantities of radiant heat downwardly towards the surface for softening of it while traveling along the roadway. These heaters consist basically of porous fire bricks through which an air/propane mixture passes and on the surface of which it burns. Each heater also has porous side walls that project closer to the roadway surface than the main bricks and are supplied with air for forming a downward curtain of air to inhibit sideways escape of heat from the region beneath the heater. The heaters are assembled in banks that are spaced apart from each other in the direction of travel. This spacing can be adjusted. Each pair of adjacent banks is bridged by heat deflectors that help to provide heat soak areas between the heater banks.
U.S. Pat. No. 4,594,022, to Jeppson, provides for a microwave energy reflecting zone below the surface of pavement. The reflecting zone is established within the range that microwave energy can penetrate. The reflective zone, which is formed of electrically conductive material, results in energy and cost savings in subsequent paving or pavement repair operations that involve microwave heating of thermoplastic pavement. The heating is concentrated in within the localized upper portion of the pavement. Different microwave heating patterns may be employed.
U.S. Pat. No. 4,619,550, to Jeppson, teaches a method for economically heating fragmented old aspahltic concrete by temporarily separating larger pieces from the smaller fragments, generating heat internally within the large pieces with penetrating microwave energy, separately heating the smaller fragments by exposure to hot gas, and then recombining and remixing the separately heated components.
U.S. Pat. No. 4,793,730, to Butch, reveals a method and apparatus for renewing the surface of asphaltic paving at low cost and for immediate reuse. The asphalt surface is heated to about 300° to 500° F. The surface is broken to a depth of about two inches and the lower material thoroughly mixed in situ with the broken surface material. After mixing the material is further heated to fuse the heated mixture into a homogeneous surface. The surface is screed for leveling and compacted by a road roller. The process features a steam manifold for heating the asphalt, transversely reciprocating breaker bars having teeth adjusted to the desired depth, and a second steam manifold for reheating the mixed material.
U.S. Pat. No. 5,366,320, to Hanlon et al., discloses an improved screed for leveling abrasive paving material on a road surface. The screed is highly abrasion resistant and loses much less heat during shutdown periods than a steel screed because it is formed of a composite that includes a chromium-carbide alloy. The alloy has a Brinell hardness in the range of 550 to 600 and a low coefficient of friction. The screed features a curved leading edge to prevent asphalt material from welling up over the front of the screed as it travels along the surface of the asphalt pavement.
U.S. Pat. No. 5,556,225, to Marino, provides for a method of immediately repairing multiple backfilled utility cut trenches, potholes, and other discontinuities in asphalt pavement, at any ambient temperature, in which the pavement discontinuity is bridged by layers of heated virgin bituminous concretes of different grades, each layer including aggregate stone mixed with liquid asphalt binder. Alternatively, substantially non-polymerized thermoplastic bituminous concretes of different grades may be used to form the bridging layers, each layer including aggregate stone mixed with a liquid asphalt binder and preferably also containing fractions of n-pentane soluble asphalts and being repetitively softenable in response to repetitive applications of infrared radiation.
U.S. Pat. No. 6,371,689, to Wiley, teaches a method and apparatus for heating an asphalt-paved road surface by forcing gases heated by a heater against the road surface and then returning those gases to the heater for reheating and recirculation, wherein the temperature of the returning gases is measured by a temperature sensor, and the heater is automatically adjusted to that the temperature of the gases is automatically decreased as the temperature of the returning gases increases. This prevents damage to the asphalt and premature rupturing of the road surface.
It is known that some materials may be worked by friction heating, for example friction welding. Rotary friction welding was the first of the friction processes to be developed and used commercially to join work pieces together. The simplest mechanical arrangement for continuous-drive rotary friction welding involves two work pieces being brought into axial alignment. One of the pieces is rotated while the other is advanced into contact under a known axial pressure. Rotational contact continues for a time sufficient for the temperature to plasticize the metal interface in the region of the joint. Having achieved this condition, the rotating work piece is stopped while the pressure is either maintained or increased to consolidate the joint.
Another method of friction welding is known as inertia welding. Inertia welding differs from rotary welding in that the rotating work piece is attached to a flywheel which is accelerated to a known rpm. The flywheel is then disconnected from its driving mechanism. The spinning flywheel is then brought into contact with the stationary work piece in such a manner that the frictional braking action produces the required heat for welding.
U.S. Pat. No. 6,732,900, to Hansen et al., describes a process known as friction stir welding. The process involves welding component parts together using friction heat generated at the welding joint to form a plasticized region that solidifies to join work piece sections. Welding is performed by inserting a probe into a joint between the work piece sections. The probe includes a pin that is inserted into the joint and shoulder, which is urged against the surfaces of the work pieces. The pin and shoulder spin together to generate friction heat to form the plasticized region along the joint for the welding operation. Hansen further discloses a friction stir welding spindle with an axially displaceable shaft.
U.S. Pat. No. 6,779,704, to Nelson et al., teaches a process for frictional stir welding metal matrix composites, ferrous alloys, non-ferrous alloys, and super alloys using superabrasive materials.
The applicants were surprised to discover that aggregate asphalt pavement may be worked, i.e. heated and decomposed, using a frictional rotary tool in place of the conventional heating and mechanical decomposition systems of the past.